Apparatus for casting a film

ABSTRACT

The apparatus for containing the pool of coating material is mounted on a pivoted backing plate which is arranged for a pivotal movement between two side plates. A slot is provided at the bottom of the pool to allow a strip of material to enter the bottom of the pool and travel upwardly along the backing plate and over considerable guide means adjacent the pivot point for the backing plate. Adjustable stops are provided for holding the backing plate at various angles relative to the vertical so that as the strip of material passes through the pool along the backing plate the amount of coating material picked up by the strip of material will vary depending upon the angle of the backing plate.

United States Patent Cato, Jr. et al.

[54] APPARATUS FOR CASTING A FILM [72] inventors: Russel L. Cato, Jr., Raleigh, NC; Percy D. Leonard, Jr., U. S. Air Force; Robert D. Smith, Raleigh, NC.

[73] Assignee: Corning Glass Works, Corning, N .Y.

[22] Filed: Nov. 7, 1969 [21] Appl. No.: 874,951

Related U.S. Application Data {62} Division of Ser. No. 626,560, Mar. 28, 1967, aban- 3,659,990 51 May 2,1972

FOREIGN PATENTS OR APPLICATIONS 269,508 8/1966 Australia ..21 1/150 Primary Examiner-Robert D. Baldwin Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak 57] ABSTRACT The apparatus for containing the pool of coating material is mounted on a pivoted backing plate which is arranged for a pivotal movement between two side plates. A slot is provided at the bottom of the pool to allow a strip of material to enter the bottom of the pool and travel upwardly along the backing plate and over considerable guide means adjacent the pivot point for the backing plate. Adjustable stops are provided for holding the backing plate at various angles relative to the vertical so that as the strip of material passes through the pool along the backing plate the amount of coating material picked up by the strip of material will vary depending upon the angle of the backing plate.

3 Claims, 8 Drawing Figures PATENTEDMAY 2 I972 SHEET 1 [IF 2 mvmroxs RUSSEL L. cnro .m. PERCY o. mormho ROBERT 0. sum

BY wu zglh ATTORNEY! PATENTEBHAY 2 1912 3, 659 9S0 SHEET 2 BF 2 ATTORNEYS APPARATUS ron CASTING A FILM CROSS REFERENCE TO RELATED APPLICATIONS This application is a division of application Ser. No. 626,560 filed Mar. 28, 1967 in the names of Russel L. Cato, J r., Percy D. Leonard, Jr., and Robert D. Smith and entitled Method and Apparatus For Casting a Film, now abandoned.

This invention pertains to apparatus for casting a film, and particularly to casting thin films while controlling the thickness of the film cast.

It is known in the prior art to cast a film of material on a moving belt in which the belt forms one wall of a pool of material to be cast. In one known prior art embodiment, a doctor blade is utilized to control the thickness of the film cast. However, with such arrangement buildup of the material being cast behind the doctor blade causes a variation in the thickness of the cast material. Furthermore, different viscosity materials create problems in obtaining a uniform thickness cast film using doctor blade techniques. The prior known methods of casting a film on a moving belt were very dependent on the skill of a operator to obtain constant thickness control, since the operator controlled the doctor blade.

The invention resides in the use of a moving belt defining one side of a casting material pool and moving upwardly at a variable angle and at a variable speed on which is cast a controlled thickness film. The angle of movement of the belt and the speed of the belt may be varied to control the thickness within a desired degree. Furthermore, the speed of the belt may be variably controlled in response to a thickness detecting gauge. This method is not dependent on operator skill and produces a film with thickness variation within very small limits. The film of material cast is removed from the belt after solidifying.

Other features of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode which has been contemplated of applying that principle. The angle of the belt may be varied by providing a container for the casting material which is provided with an entrance slot for the moving belt adjacent the bottom thereof so that the belt will be moved upwardly through the pool. The container is pivotally mounted to enable the angle of the belt with respect to the vertical to be varied.

IN THE DRAWINGS FIG. I is a side elevation view of the apparatus used for practicing the method of this invention.

FIG. 2 is a top plan view of the apparatus shown in FIG. 1.

FIG. 3 is a sectional view taken along line 3-3 of FIG. 1 with a portion removed for the sake of clarity.

FIG. 4 is a sectional view taken along line 4--4 of FIG. 3.

FIG. 5 is a sectional view similar to FIG. 4 showing the different angle of inclination of the cast film supporting belt.

FIG. 6 is a perspective view, with some components broken away, showing the arrangement of the coating material containing pool.

FIG. 7 is an end elevation view of a coating thickness monitoring gauge.

FIG. 8 is a side elevation schematic view of a take-up arrangement for the supporting belt and the cast film.

Referring to FIGS. 1 and 2, the apparatus for practicing the method of this invention includes a coating table 10 having a supporting framework 12 and a flat horizontal table top I4. A pool P of the material to be cast is carried at one end of the table and a belt B runs through the pool forming one side wall of the pool at a variable angle to the vertical.

The belt is unwound from a roll 15 carried by roll support 16 from one end of the frame, passes upward and then horizontally over the table 14, and is taken up at a take-up roll 17 supported from roll support 18 at the other end of the frame. The speed of the belt is controlled by drive rollers 19, while the roll on support 16 is braked.

The angle the belt B forms with a vertical plane is controlled by moving a belt support plate 20 about a pivot shaft 22 and holding it in adjusted position by means of side plates 24 having adjustment holes 26 therein.

FIGS. 4-6 show the arrangement in detail and it is noted that the pool P is confined, at least on one side, by the belt B and on three other sides by member 25. Member 25 has a back piece 27, side pieces 28 and tits with alignment lugs 30 attached to plate 20 and is secured to plate 20 by suitable screws 32. The angle of plate 20 to a vertical plane is determined by screws 34 extending through the side plates 24 and selected holes 26. As can be seen with reference to FIGS. 4 and 5, the angle of the belt B with respect to a vertical plane may be varied by swinging plate 20 about shaft 22.

The pool P may be provided with a cover 36 shown in FIGS. 4 and 5 in three flexible sections. This cover covers the pool and the first part of the belt during the coating to act as a dust cover and to maintain conditions surrounding the casting pool P.

On movement of the belt upwardly over plate 20, the casting material in pool P adheres to the surface of the belt and forms a film of constant thickness. As the belt turns and moves vertically over the top of table 14, it is dried either by a heater 40 under the top of table 14 or by auxiliary heating means, such as infrared lamps 42 supported from bar and column supports 44 above the film, or both.

At the exit end of the table, the belt B is broken over a sharp edge 46 to be taken up at a constant rate by take-up rolls 19. The then cast film F separates from the belt and tends to go on a straight line where it may either be passed onto another support table or taken up itself in a take-up arrangement with a suitable interleaving paper material, such as material I, from roll 48. The combination of film and interleaf material is wound up on roll 50. Both rolls 48 and 50 are supported from a bracket 52 from framework 12, and take-up roll 50 and interleaving roll 48 are controllably driven by motor 54 and clutch arrangement 56 with belts 58.

FIGS. 1 and 8 show the take-up rolls 19 for the belt going at a constant speed so the diameter of the material on the roll 17 does not vary the speed of the belt B.

A thickness measuring gauge 60, shown in FIGS. 1, 2 and 7, is used to monitor the thickness of the film F cast on the belt B. This may be a commercially available X-ray gauge 62 mounted above the belt and film with a source of X-ray emitting material 64 below the belt and the gauge may be reciprocated transverse to the belt, as illustrated in FIG. 7. An output from the gauge may be utilized to control the drive of the belt so as to control and monitor the thickness of the film by feedback from the measured thickness to control the speed of the belt.

The material to be cast may be placed in pool P in either batch form or continuously. The belt B may be continuously driven until no more material is in the pool, or may be stopped over heater 40. The film F may be taken off with an interleav ing roll or may be taken off on a separate table.

It has been found that the thickness of the cast material is proportional to the viscosity of the coating material, the belt speed, the density of the coating material, and the angle that the belt moves with respect to the vertical. This angle may be varied and the belt speed may be varied to control the thickness (assuming that the viscosity and density are held constant). Since density and viscosity vary with temperature, constant temperature devices may be employed on the reservoir. This invention provides the means for varying either the belt speed or the angle or both to control the thickness of the cast film. The movement of the belt within the pool or reservoir creates a current for stirring the casting material, which prevents the material from settling. It is important to note that in operation, the thickness of the material is constant and independent of small variables and ripples in the surface of belt.

In one example of the use of the process, the liquid to be cast is a latex base suspension of 94 percent alumina. The belt is a Mylar belt and the angle of the belt to the vertical is 60.

The belt is driven at feet per minute and the viscosity of the material being cast is 2,000 cp. The material is dried while the belt is stationary at the top of the table for 2 hours at 65 C. and a green ceramic material of a cast thickness of 0.030 inch results. The green ceramic material may be later cut, punched, fired and glazed to provide high dielectric strength ceramic plates of uniform density for use as substrates for microcircuits.

The use of this invention has provided a method of casting material having a thickness variation to about 3 percent overall, whereas with the use of the prior method by applicant using doctor blades, the total overall thickness control was 20 percent from nominal. The employment of this method has increased the acceptable cast films from 60 percent to over 95 percent of those cast.

With this method, the film thickness is controlled to a very high degree of precision without dependence on a doctor blade or on the skill of an operator. The thickness of the film is independent of ripples or variables in the surface of the belt. That is, the film is the same thickness even if the belt varies in thickness. The movement of the belt keeps the material in pool P agitated and keeps it from settling and causing viscosity changes.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. An apparatus for casting a film of predetennined thickness on a moving belt comprising:

container means for holding a casting pool having at least one smooth wall for supporting a moving belt and a pair of stationary spaced apart side plates transversely disposed at opposite ends of said wall;

a feed roller;

pivot shaft means extending between said side plates and fixedly mounting said feed roller with respect to said side plates;

means pivotably securing said support wall to said pivot shaft means for pivotal movement between said side walls;

means for maintaining said support wall at various angles with respect to a vertical plane between said side walls, and

slot means in said container means adjacent the lowermost end thereof to provide for the entry of said moving belt into said casting pool along said support wall.

2. An apparatus as set forth in claim 1 further comprising means for feeding a belt upwardly through said casting pool and means for varying the speed at which said belt moves.

3. An apparatus as set forth in claim 2, further comprising a flexible cover means including a pair of relatively pivoting members for covering said casting pool and belt.

I i i t 

1. An apparatus for casting a film of predetermined thickness on a moving belt comprising: container means for holding a casting pool having at least one smooth wall for supporting a moving belt and a pair of stationary spaced apart side plates transversely disposed at opposite ends of said wall; a feed roller; pivot shaft means extending between said side plates and fixedly mounting said feed roller with respect to said side plates; means pivotably securing said support wall to said pivot shaft means for pivotal movement between said side walls; means for maintaining said support wall at various angles with respect to a vertical Plane between said side walls, and slot means in said container means adjacent the lowermost end thereof to provide for the entry of said moving belt into said casting pool along said support wall.
 2. An apparatus as set forth in claim 1 further comprising means for feeding a belt upwardly through said casting pool and means for varying the speed at which said belt moves.
 3. An apparatus as set forth in claim 2, further comprising a flexible cover means including a pair of relatively pivoting members for covering said casting pool and belt. 